Applied Surface Science (v.281, #C)
Editorial Board (ii).
Preface by Peter Petrik (1).
Towards FDTD modeling of spectroscopic ellipsometry data at large angles of incidence by King Tai Cheung; Yishu Foo; Chap Hang To; Juan Antonio Zapien (2-7).
► Quantitative optical simulation of thin film with sub-monolayer resolution ► Relationship between MSE and AoI for SE data by FDTD ► Addressed and solve problems (e.g. artifact resonance in bloch boundary condition (BBC)) in achieving quantitative optical modeling at large AoI of 70°.Precise modeling of the spectroscopic ellipsometry (SE) response of arbitrary near-planar structures by finite-difference time-domain method (FDTD) is desirable for developing a general method for advanced quantitative optical characterization of complex samples. Such a synergetic SE–FDTD approach would be of great interest for fundamental applications such as, the understanding and characterization of nanostructure and plasmonic materials, and industrial applications providing additional tools for optical metrology. For both cases it is of great interest to achieve sub-monolayer modeling precision at large angles of incidence (AoI) where SE measurements are usually more sensitive. To advance this goal, we report the correlation between mean square error (MSE) and AoI studied for prototypical thin film structures. We show that an observed increase in FDTD simulation errors at large AoI can be correlated to the development of spurious resonances, resulting from the use of periodic boundary conditions. A solution to this problem is proposed resulting in ∼10× improved MSE values. It is believed that the combined FDTD–SE approach presented in this contribution could enable the SE description of increasingly complex structures thus paving the way for a powerful synergetic and complimentary SE–FDTD approach to study the optical properties at the sub-wavelength scale of complex nanostructures.
Keywords: Spectroscopic ellipsometry; SE; Finite-difference time-domain; FDTD; Optical modeling; Nanostructure characterization;
Medium energy ion scattering for the high depth resolution characterisation of high-k dielectric layers of nanometer thickness by J.A. van den Berg; M.A. Reading; P. Bailey; T.Q.C. Noakes; C. Adelmann; M. Popovici; H. Tielens; T. Conard; S. de Gendt; S. van Elshocht (8-16).
► The essence of medium energy ion scattering (MEIS) for nanolayer analysis is given. ► MEIS is applied to characterise high-k nanolayers and (DRAM) multilayer structures. ► MEIS is shown to give quantitative composition depth profiles and layer thicknesses. ► MEIS is shown to identify the nature & extent of layer intermixing and segregation.Medium energy ion scattering (MEIS) using, typically, 100–200 keV H+ or He+ ions derives it ability to characterise nanolayers from the fact that the energy after backscattering depends (i) on the elastic energy loss suffered in a single collision with a target atom and (ii) on the inelastic energy losses on its incoming and outgoing trajectories. From the former the mass of the atom can be determined and from the latter its depth. Thus MEIS yields depth dependent compositional and structural information, with high depth resolution (sub-nm near the surface) and good sensitivity for all but the lighter masses. It is particularly well suited for the depth analysis of high-k multilayers of nanometer thickness. Accurate quantification of the depth distributions of atomic species can be obtained using suitable spectrum simulation.In the present paper, important aspects of MEIS including quantification, depth resolution and spectrum simulation are briefly discussed. The capabilities of the technique in terms of the high depth resolution layer compositional and structural information it yields, is illustrated with reference to the detailed characterisation of a range of high-k nanolayer and multilayer structures for current microelectronic devices or those still under development: (i) HfO2 and HfSiO x for gate dielectric applications, including a TiN/Al2O3/HfO2/SiO2/Si structure, (ii) TiN/SrTiO3/TiN and (iii) TiO2/Ru/TiN multilayer structures for metal–insulator–metal capacitors (MIMcaps) in DRAM applications.The unique information provided by the technique is highlighted by its clear capability to accurately quantify the composition profiles and thickness of nanolayers and complex multilayers as grown, and to identify the nature and extent of atom redistribution (e.g. intermixing, segregation) during layer deposition, annealing and plasma processing. The ability makes it a valuable tool in the development of the nanostructures that will become increasingly important as device dimensions continue to be scaled down.
Keywords: Medium energy ion scattering analysis; High resolution depth profiling; High-k nanolayers; Metal–insulator–metal capacitor (MIMcap) layers;
Shape, size, and atomic composition analysis of nanostructures in 3D by Rutherford backscattering spectrometry by Zsolt Zolnai (17-23).
The emergence of novel micro- and nanofabrication tools lead to the targeted research of highly ordered three-dimensional nanosystems, constructed from regular building blocks like spheres, cylinders, bricks, pyramids, which can be used in a wide range of applications. As a consequence, the exploration of the potential and limits of efficient analytical techniques to characterize structured nanosystems became a significant task. In this work the scope of conventional Rutherford backscattering spectrometry (RBS) analysis is extended to investigate highly ordered periodic nanostructures in three dimensions. Hexagonally arranged spherical and ellipsoidal silica particles, rectangular gold nano-arrays, and embedded structures in Si substrates and silica particles are analyzed. It is shown that the shape of the measured spectra can be correlated with the shape of individual nano-objects through geometrical considerations. The evaluation of the recorded data for different sample tilt angles can be carried out with the Monte-Carlo type 3D simulation model cell concept considering the details of the applied measurement geometry. It is demonstrated that macrobeam 3D-RBS can provide valuable information on the shape, size, spacing, and atomic composition of nanostructured samples as well as on nanoscale atomic transport processes and consequently, it can be utilized as a highly precise, non-destructive characterization tool for nanotechnology.
Keywords: 3D Rutherford backscattering spectrometry; Ion beam analysis; Periodic nanostructures; Nanosphere lithography; Nanopatterning;
Kelvin probe force microscopy for characterizing doped semiconductors for future sensor applications in nano- and biotechnology by Heidemarie Schmidt; Stefan Habicht; Sebastian Feste; Anne-Dorothea Müller; Oliver G. Schmidt (24-29).
Kelvin probe force microscopy (KPFM) is one of the most promising non-contact electrical nanometrology techniques to characterize doped semiconductors. By applying a recently introduced explanation of measured KPFM signals, we show the applicability of KPFM to determine and control surface-near electrostatic forces in planar doped silicon and in doped silicon nanostructures. Surface-near electrostatic forces may be used for the immobilization of nano- and biomaterials in future sensor applications in nano- and biotechnology. Additionally, the influence of the electrostatic potential distribution in doped semiconductor nanostructures, e.g. in horizontal Si nanowires, and its influence on the surface-near electrostatic forces are discussed. It is explained how drift and diffusion of injected electrons and holes in intrinsic electric fields influence the detected KPFM signal. For example KPFM is successfully employed to locate p+p and n+p junctions along B-doped and As-doped p-Si nanowires, respectively. As an outlook the physical immobilization and the transport of biomaterials above arrays of separately addressable doped semiconductor cells will be discussed.
Keywords: Kelvin probe force microscopy; Electrical biosensors; Doped semiconductors; Biomaterials; Immobilization; Transport;
Optical and microstructural characterisation of Au–Sn and Cu–Sn diffusive layers by A.A. Wronkowska; G. Czerniak; A. Wronkowski; Ł. Skowroński (30-37).
► We determined phase composition, optical and electrical properties of Au–Sn and Cu–Sn ultra-thin films. ► The samples were characterised using the XRD, SEM, SE and transmittance measurements. ► Creation of intermetallic phases at room temperature was revealed in both types of samples. ► The effective complex dielectric functions and optical conductivity were determined. ► The optical resistivity of multiphase films agreed reasonably with the dc-resistivity results.Phase composition, crystallinity, optical and electrical properties were determined for Au–Sn and Cu–Sn ultra-thin films produced by sequential evaporating and co-depositing of metals on glass plates in a vacuum. Thickness of Sn films grown on top of Au(Cu) nanolayers (d Au(Cu) = 20 nm) was varied to obtain different atomic concentration ratios of Au(Cu)-rich diffusive samples up to 1:1. The samples were characterised using the XRD, SEM, spectroscopic ellipsometry and transmittance measurements. The XRD patterns indicated creation of AuSn and AuSn2 intermetallic phases at room temperature in both types of Au–Sn samples, formation of Cu6Sn5 compound in bilayer Sn/Cu samples and Cu10Sn3 intermetallic in the co-deposited Sn–Cu film. There was observed a substantial influence of morphology and phase composition on the effective complex dielectric functions and optical conductivity of the multiphase films, determined using the transmittance and variable angle spectroscopic ellipsometry measurements in the photon energy range of 0.6–6.5 eV. Adopting the Drude–Lorentz parameterisation approach to optical spectra enabled to extract contributions related to the free-carriers, interband transitions and plasmonic effects. The optical resistivity agreed reasonably with the dc-resistivity results, which changed approximately from 17.5 μΩ cm to 26 μΩ cm and from 24 μΩ cm to 96 μΩ cm for investigated Au–Sn and Cu–Sn systems, respectively.
Keywords: Interdiffusion in nanoscale solids; Intermetallic compounds; Dielectric function; Optical resistivity; Spectroscopic ellipsometry; X-ray diffractometry;
Microstructure strengthening mechanisms in an Al–Mg–Si–Sc–Zr equal channel angular pressed aluminium alloy by Marcello Cabibbo (38-43).
► Proof stress modelling. ► Model well agreed to the measured proof stress. ► A new microstructure strengthening, i.e. Moiré boundary, was introduced.Microstructure dislocation strengthening mechanisms in severely deformed aluminium strongly depend on the different boundary evolutions. Thereafter, models of proof stress determination should take into account the different nature of the boundaries that form during severe plastic deformation. In the last few decades, Hall–Petch modified relationship and other proof stress modelling were extensively discussed. This paper deals with further insights into the Hansen's and other authors approach to the modelling of aluminium poof stress after equal channel angular pressing. The present model is based on a detailed transmission electron microscopy microstructure characterization of the different strengthening contributions in an age-hardened Al–Mg–Si–Sc–Zr alloy.
Keywords: Strengthening mechanisms; Proof stress; TEM; Moiré fringe boundary; ECAP;
Effect of ECAP processing on corrosion resistance of AE21 and AE42 magnesium alloys by P. Minárik; R. Král; M. Janeček (44-48).
► Corrosion resistance in AE21 and AE42 magnesium alloys were studied. ► ECAP processing has a strong effect on corrosion properties and microstructure. ► The ECAP processing resulted in ultra-fine grained structure in AE21 and AE42 alloys. ► The corrosion resistance after ECAP decreased in AE21, contrary increased in AE42. ► The explanation of such inconsistency was suggested.Corrosion properties of AE21 and AE42 magnesium alloys were investigated in the extruded state and after subsequent 8 passes of Equal Channel Angular Pressing (ECAP) via route Bc, by Electrochemical Impedance Spectroscopy (EIS) in 0.1 M NaCl solution. The resulting microstructure was observed by the Transmission Electron Microscope (TEM) and the Scanning Electron Microscope (SEM). Corrosion layer created after 7 days of immersion was observed by (SEM) in order to explain different evolution of the corrosion resistance after ECAP processing in both alloys. It was found that Al-rich Al11RE3 dispersed particles (present in both alloys) strongly influence the corrosion process and enhance the corrosion resistance. Ultra-fine grained structure was found to reduce the corrosion resistance in AE21. On the other hand, the microstructure of AE42 after ECAP and particularly the better distribution of the alloying elements in the matrix enhance the corrosion resistance when compared to the extruded material.
Keywords: Magnesium; Corrosion; Extrusion; ECAP; Grain refinement;
Color change of Blue butterfly wing scales in an air – Vapor ambient by Krisztián Kertész; Gábor Piszter; Emma Jakab; Zsolt Bálint; Zofia Vértesy; László Péter Biró (49-53).
► We report optical gas sensing on butterfly wing scale nanostructures. ► The Polyommatinae species in the study possesses “pepper-pot” structure. ► The concentration dependence of the signal amplitude is close to linear. ► The sensitivity is increasing with the decrease of the sample temperature.Photonic crystals are periodic dielectric nanocomposites, which have photonic band gaps that forbid the propagation of light within certain frequency ranges. The optical response of such nanoarchitectures on chemical changes in the environment is determined by the spectral change of the reflected light, and depends on the composition of the ambient atmosphere and on the nanostructure characteristics. We carried out reflectance measurements on closely related Blue lycaenid butterfly males possessing so-called “pepper-pot” type photonic nanoarchitecture in their scales covering their dorsal wing surfaces. Experiments were carried out changing the concentration and nature of test vapors while monitoring the spectral variations in time. All the tests were done with the sample temperature set at, and below the room temperature. The spectral changes were found to be linear with the increasing of concentration and the signal amplitude is higher at lower temperatures. The mechanism of reflectance spectra modification is based on capillary condensation of the vapors penetrating in the nanostructure. These structures of natural origin may serve as cheap, environmentally free and biodegradable sensor elements. The study of these nanoarchitectures of biologic origin could be the source of various new bioinspired systems.
Keywords: Butterfly wing scale; Photonic nanoarchitecture; Photonic crystal; Gas sensor;
Evaluation of the functionality of biodegradable polymeric platforms for drug delivery systems by M. Gioti; V. Karagkiozaki; A. Basgiouraki; P.G. Karagiannidis; S. Logothetidis (54-59).
We present the development of a drug-loaded triple-layer platform consisting of thin film biodegradable polymers, in a properly designed form for the desired gradual degradation. Poly(dl-lactide-co-glycolide) (PLGA (65:35), PLGA (75:25)) and polycaprolactone (PCL) were grown by spin coating technique, to synthesize the platforms with the order PCL/PLGA (75:25)/PLGA (65:35) that determine their degradation rates. The outer PLGA (65:35) layer was loaded with dipyridamole, an antiplatelet drug. Spectroscopic ellipsometry (SE) in the Vis-far UV range was used to determine the nanostructure, as well as the content of the incorporated drug in the as-grown platforms. In situ and real-time SE measurements were carried out using a liquid cell for the dynamic evaluation of the fibrinogen and albumin protein adsorption processes. Atomic force microscopy studies justified the SE results concerning the nanopores formation in the polymeric platforms, and the dominant adsorption mechanisms of the proteins, which were defined by the drug incorporation in the platforms.
Keywords: Drug delivery; Spectroscopic ellipsometry; Biodegradable polymers; Protein adsorption; Atomic force microscopy;
Magnetic iron oxide nanoparticles as drug delivery system in breast cancer by A. Marcu; S. Pop; F. Dumitrache; M. Mocanu; C.M. Niculite; M. Gherghiceanu; C.P. Lungu; C. Fleaca; R. Ianchis; A. Barbut; C. Grigoriu; I. Morjan (60-65).
The effect of VB1-loaded nanoparticles on MCF-7 tumor cells proliferation: comparison of VB1-coated and uncoated NPs and free VB1.Display Omitted► Iron oxide nanoparticles with high magnetization and superparamagnetic properties were produced by laser pyrolysis. ► NPs internalization in the cytoplasm has a concentration dependent anti proliferative effect on MCF-7 tumor cells. ► The loading mechanism of Violamycine B1 on NP is assumed to rely on the electrostatic interactions. ► The anti-tumor activity of VB1 loaded on NP was maintained but the apoptosis process is delayed. ► NP drug delivery system should provide more drug accumulation at tumor site reducing the side effects of chemotherapy.Present work was focused on producing improved iron oxide nanoparticles for targeted drug delivery in breast cancer. Nanometric-sized iron oxide particles were synthesized by laser pyrolysis and were morphologically/structurally characterized. These new nanoparticles were compared with some commercial, chemically prepared iron oxide ones. Cytotoxicity and the anti-proliferation effects of nanoparticles were tested in vitro on the breast adenocarcinoma cell line MCF-7. Nanoparticles were further coated with the antracyclinic antibiotic Violamycine B1 and tested for the anti-tumor effect on MCF-7 cells. The nanoparticles produced by us seem more effective in vitro than the commercial ones, with respect to cellular uptake and VB1 delivery. Violamycine B1 bound on nanoparticles is as efficient as the free form, but is better delivered into tumor cells.
Keywords: Magnetic nanoparticles; Drug delivery; Laser pyrolysis; Nanotoxicity; Iron oxide nanoparticle; Violamycine B1; VB1;
Investigation of thin polymer layers for biosensor applications by András Saftics; Emil Agócs; Bálint Fodor; Dániel Patkó; Péter Petrik; Kai Kolari; Timo Aalto; Péter Fürjes; Robert Horvath; Sándor Kurunczi (66-72).
► A polyimide waveguide material was investigated in aqueous solutions by in situ ellipsometry for biosensor applications. ► The large drift of the polyimide in solutions revealed water susceptibility and the need for suitable protection. ► The TiO2 ALD coat was promising as a shielding layer on the polyimide. ► The stable polyethyleneimine layer was proved on the polyimide which can be used as an immobilization layer in biosensors.Novel biosensors made of polymers may offer advantages over conventional technology such as possibility of mass production and tunability of the material properties. With the ongoing work on the polymer photonic chip fabrication in our project, simple model samples were tested parallel for future immobilization and accessing conditions for applications in typical aqueous buffers. The model samples consist of a thin, high refractive index polyimide film on top of TEOS on Si wafer. These model samples were measured by in situ spectroscopic ellipsometry using different aqueous buffers. The experiments revealed a high drift in aqueous solutions; the drift in the ellipsometric parameters (delta, psi) can be evaluated and presented as changes in thickness and refractive index of the polyimide layer. The first molecular layer of immobilization is based on polyethyleneimine (PEI). The signal for the PEI adsorption was detected on a stable baseline, only after a long conditioning. The stability of polyimide films in aqueous buffer solutions should be improved toward the real biosensor application. Preliminary results are shown on the possibilities to protect the polyimide. Optical Waveguide Lightmode Spectroscopy (OWLS) has been used to demonstrate the shielding effect of the thin TiO2 adlayer in biosensor applications.
Keywords: Photonic biosensor; Polymer; Polyimide; Drift; In situ ellipsometry; Optical properties;
Characterization of electric discharge machining, subsequent etching and shot-peening as a surface treatment for orthopedic implants by Josef Stráský; Jana Havlíková; Lucie Bačáková; Petr Harcuba; Mansour Mhaede; Miloš Janeček (73-78).
► Surface treatment of Ti alloy by electric discharge machining, etching and shot peening. ► Surface topography enhances the proliferation of osteoblast-like cells. ► Shot peening improves poor fatigue performance after electric discharge machining. ► Proposed three-step surface treatment is well applicable in orthopedics.Presented work aims at multi-method characterization of combined surface treatment of Ti–6Al–4V alloy for biomedical use. Surface treatment consists of consequent use of electric discharge machining (EDM), acid etching and shot peening. Surface layers are analyzed employing scanning electron microscopy and energy dispersive X-ray spectroscopy. Acid etching by strong Kroll's reagent is capable of removing surface layer of transformed material created by EDM. Acid etching also creates partly nanostructured surface and significantly contributes to the enhanced proliferation of the bone cells. The cell growth could be positively affected by the superimposed bone-inspired structure of the surface with the morphological features in macro-, micro- and nano-range. Shot peening significantly improves poor fatigue performance after EDM. Final fatigue performance is comparable to benchmark electropolished material without any adverse surface effect. The proposed three-step surface treatment is a low-cost process capable of producing material that is applicable in orthopedics.
Keywords: Ti–6Al–4V alloy; Surface treatment; Cell proliferation; Fatigue performance; Orthopedics;
The mechanism of the photoluminescence changes in bio-conjugated CdSe/ZnS quantum dots by L. Borkovska; N. Korsunska; T. Stara; O. Kolomys; V. Strelchuk; O. Rachkov; T. Kryshtab (79-83).
► The changes in luminescence and Raman spectra in CdSe/ZnS quantum dots (QDs) during storage have been studied. ► The QD luminescence band blue shifts, broadens and decreases in intensity. ► The CdSe (LO) peak shifts to the low frequency region and broadens. ► The changes are ascribed to QD oxidation, which decreases the QD size. ► Bio-conjugation is supposed to promote QD oxidation.The change of the photoluminescence (PL) and optical characteristics in non-conjugated and conjugated with S6K2 antibody CdSe/ZnS core/shell quantum dots (QDs) during storage in air has been studied by the conventional PL, micro-PL and micro-Raman techniques. The QDs dried on a crystalline Si substrate were kept in the darkness and under illumination. In the PL spectra, the storage resulted in a blue shift of PL peak position, in the increasing of the full width at a half maximum (FWHM) of the PL band and in the decreasing of the PL intensity. In the Raman spectra, the shift of the CdSe LO peak position to the low frequency region and the increasing of its FWHM were observed. The transformations in the PL and optical characteristics correlate with each other and are found to be the largest in bio-conjugated QDs stored under illumination. The increase of the light intensity accelerated the changes occurred during storage. An oxidation of the QD core, which decreases the QD size, is supposed to be responsible for observed transformations. The bio-conjugation is assumed to promote QD oxidation that results in different PL peak position in stored non-conjugated and bio-conjugated QDs. The mechanism of the effect is discussed.
Keywords: Quantum dots; Bio-conjugation; micro-Photoluminescence; micro-Raman;
Surface modification methods to improve behavior of biosensor based on imaging ellipsometry by Yu Niu; Gang Jin (84-88).
Surface modifications not only perform functions as ligand immobilization and biosensing interface formation, but also play a crucial role for inhibiting noise and enhance biosensor signal. After years of development, several surface modification methods designed for the biosensor based on imaging ellipsometry have become more and more practical and already been successfully implemented in the detection of various biomolecules. Some typical surface modification approaches are reviewed.
Keywords: Biosensor; Imaging ellipsometry; Surface modification;
Far field optical nanoscopy: How far can you go in nanometric characterization without resolving all the details? by Paul C. Montgomery; Bruno Serio; Freddy Anstotz; Denis Montaner (89-95).
► We present an original classification scheme of optical nanoscopy techniques. ► We briefly review diffraction limited, far field optical nanoscopy techniques. ► Such techniques can be used in nano-characterization of nano- and biomaterials. ► The detection and measurement of nano-structures is possible over wide fields (mm). ► The advantages are real time analysis, huge amounts of data and non-destructiveness.In the development of nanomaterials and biomaterials, new characterization techniques are required that overcome the challenges presented by the increasing dimensional ratio between the different entities to be studied and the growing complexity introduced by the use of heterogeneous materials and technologies. Diffraction limited far field optical nanoscopy techniques are receiving growing interest because of their ability to detect nanometer structures over very large fields and at high speed. We present a classification scheme of the different types of optical nanoscopy techniques. In particular, we highlight four categories of far field diffraction limited techniques based on increasing the contrast, measuring the phase, using deconvolution and using nano-markers. We demonstrate that by increasing the power of detectability, observability or measurability, a wealth of information concerning nanometric structures becomes available even though all the lateral details may not be resolved. For example, it is possible to determine the presence, the structure and orientation of nanostructures, to measure their density, position and 2D and 3D distribution and to measure nanometric surface roughness in bulk materials, surfaces, nano-layers, soft matter and cells. These techniques conserve all the advantages associated with classical imaging such as real time imaging, non-invasiveness, non-destructiveness and ease of use.
Keywords: Nanoscopy; Far field imaging; Diffraction limited; Nanomaterials; Biomaterials; Nano-characterization;
Stoichiometry dependence of the optical properties of amorphous-like In x − w Ga w Zn1−x O1+0.5x−δ thin films by A.C. Galca; G. Socol; L.M. Trinca; V. Craciun (96-99).
► Amorphous oxide thin films are synthesized by pulsed laser deposition. ► Refractive index and mass density are dependent on cations concentration. ► The functionality of the thin films depends on stoichiometry.The paper investigates the dependence of the optical properties on cation concentration of amorphous-like indium gallium zinc oxide thin films (In x − w Ga w Zn1−x O1+0.5x−δ ) with various (In + Ga)/(In + Ga + Zn) and Ga/(In + Ga) ratios obtained by pulsed laser deposition. X-ray reflectivity and spectroscopic ellipsometry thickness results were in good agreement. The proportionality between density and the refractive index in the transparency range is evidenced. The extracted physical parameters are clearly influenced by the variation of cation concentration.
Keywords: 81.15.Fg; 81.05.Gc; 61.43.Dq; 73.61.Jc; 78.66.Jg; Transparent conductive oxides; Amorphous oxide semiconductors; Thin films; X-ray reflectivity; Spectroscopic ellipsometry; Optical properties;
X-ray spectroscopic methods in the studies of nonstoichiometric TiO2−x thin films by K. Kollbek; M. Sikora; Cz. Kapusta; J. Szlachetko; K. Zakrzewska; K. Kowalski; M. Radecka (100-104).
► Thin films of TiO2−x are deposited by means of dc-pulsed reactive sputtering. ► X-ray spectroscopic techniques are used to study electronic and structural properties. ► Contribution from Ti3+ oxidation states appears in nonstoichiometric TiO2−x. ► Band gap energies derived from the optical spectra and RXES analysis are consistent.X-ray spectroscopic techniques have been used in the studies of electronic and structural properties of nonstoichiometric TiO2−x thin films obtained by reactive sputtering from Ti target. Films characterisation has been completed by means of X-ray diffraction in grazing incidence, GID, UV Raman and impedance spectroscopy, optical spectrophotometry, 1s3p Resonant X-ray Emission Spectroscopy, RXES, and X-ray Photoelectron Spectroscopy, XPS. Stoichiometric thin films of TiO2 are composed of a well-crystallised anatase–rutile mixture with the predominance of anatase while the films with higher oxygen deficit are amorphous to larger extent. Oxidation state changes from Ti4+ in stoichiometric films towards Ti3+ upon increasing departure from stoichiometric composition. This change is accompanied by the significant decrease in the electrical resistivity. The comparison of band gap energies, determined independently from optical and valence band X-ray absorption/emission spectra is good assuming direct allowed transitions.
Keywords: Titanium dioxide; Nonstoichiometric thin films; Optical properties; 1s3p(3d) RXES; XPS; XRD; Impedance spectroscopy;
Ellipsometric study of crystalline silicon hydrogenated by plasma immersion ion implantation by A. Szekeres; S. Alexandrova; P. Petrik; B. Fodor; S. Bakalova (105-108).
► We examined Si surface layers modified by plasma immersion H+ implantation (PII). ► The PII-induced changes were studied by ellipsometry in the VIS range. ► PII creates a-Si inclusions, defects and tensile stress in a thin Si surface layer. ► The PII effect on the Si layer parameters enhances with increasing the H+ fluence.The structure and the optical properties of thin Si layer hydrogenated by shallow plasma ion implantation with different fluences up to 1015 cm−2 are studied using spectroscopic ellipsometry and simulation of the distributions of the ions and implantation induced defects. The implantation was regarded to proceed into Si through the native SiO2. Two-layer optical models are applied for examination of the composition and dielectric function behavior of the formed structures. The native oxide is found to be 3 nm thick. The thickness of the Si modified layer decreased 23 to 14 nm with ion fluence due to increased formation of highly hydrogenated surface region that hinder further H-penetration into the Si bulk, especially at the highest fluence. Shifts of the features in the obtained dielectric functions related with Si interband transitions at about 3.4 and 4.2 eV are found caused by process-induced tensile stress. The modified Si region is related rather to defects created by the ion implantation process than the projected range of hydrogen ions. The overall layer modification can be characterized by a low degree of amorphization (up to 5.8%), creation of structural defects and internal tensile stress.
Keywords: Plasma-immersion implantation; Oxidation of H+ ion implanted Si; Spectroscopic ellipsometry;
Influence of doping level on shift of the absorption edge of gallium nitride films (Burstein-Moss effect) by S.N. Svitasheva; A.M. Gilinsky (109-112).
► Films of n-type GaN with different doping levels (E18-E20) were grown by ammonia MBE technique. ► Noticeable changing of energy position and slope (as broken line) of absorption edge were first revealed from ellipsometric spectra (ES). ► These features of absorption edge are impossible to find from transmittance spectra. ► Authors propose to predict electrical properties from ES using preliminary found correlation dependence between optical and electrical properties. ► It will be provided fast monitoring of expensive structures.In this ellipsometric study it was revealed possibility of observation of the absorption edge shift and changing of its slope for gallium nitride films doped by silicon. It seems to be attractive to connect specific features of Burstein-Moss shift with structural and electrical properties of films of gallium nitride in future. As well known the Burstein-Moss effect occurs when the carrier concentration exceeds conduction band edge density of states, which corresponds to degenerate doping in semiconductors.
Keywords: Ellipsometry; Optical properties; Triple alloy nitride; Doping level;
Spectroellipsometric characterization of nanocrystalline diamond layers by T. Lohner; P. Csíkvári; P. Petrik; G. Hárs (113-117).
► Deposited nanocrystalline diamond films on silicon substrate. ► Developed multilayer optical models. ► Determined film thickness, optical properties from ellipsometry.The complex refractive index and the layer thickness of nanocrystalline diamond films was determined by ex situ variable angle spectroscopic ellipsometry in the wavelength range of 191–1690 nm. During the layer depositions argon, methane and hydrogen gases were used as source gases. The combined effect of argon addition and substrate bias was investigated in the microwave plasma assisted chemical vapor deposition of diamond. Multilayer optical models were constructed for the evaluation of the measured ellipsometric spectra. The effective medium approximation and the Lorentz dispersion relation were employed for the modeling of the optical properties of the diamond films.
Keywords: Nanocrystalline diamond; Microwave plasma enhanced CVD; Spectroscopic ellipsometry; Optical modeling;
Enhancement of the photoluminescence in CdSe quantum dot–polyvinyl alcohol composite by light irradiation by L. Borkovska; N. Korsunska; T. Stara; O. Gudymenko; Ye. Venger; O. Stroyuk; O. Raevska; T. Kryshtab (118-122).
► The effect of photo-induced enhancement of deep trap photoluminescence (PL) of quantum dots (QDs) is found. ► The effect is observed in the CdSe QDs embedded in polyvinyl alcohol (PVA) film. ► The effect is caused by the increase of the activation energy of the PL thermal quenching. ► The effect is ascribed to change of QD surface defect passivation caused by photochemical transformations at the QD/PVA interface.The effect of photo-induced enhancement (more than a tenfold) of room temperature deep-trap photoluminescence (PL) in CdSe quantum dots (QDs) embedded in polyvinyl alcohol (PVA) film has been found and investigated by the PL and X-ray diffraction methods. The effect is observed under illumination of the QD/PVA composite with LED's light of 409 or 470 nm at elevated temperatures and is shown to be caused by an increase of the activation energy of thermal quenching of defect-related PL. It is shown that thermal annealing of the composite by itself stimulates polymer crystallization and produces a small increase in the intensity of both the band-edge and defect-related PL bands of CdSe QDs. It is found that the effect of illumination decreases when the annealing temperature increases from 90 °C to 120 °C because thermal annealing at 120 °C per se results in strong enhancement of room temperature deep-trap PL. The effect of photo-induced enhancement of defect-related PL is found to be irreversible and is assumed to be related to the change of QD surface defect passivation or surface defect rearrangement. This is ascribed to partial destruction of PVA matrix as a result of interaction of QD/PVA interface with photocarriers generated in the QDs due to LED's light absorption.
Keywords: Quantum dots; Polyvinyl alcohol; Photoluminescence; X-ray diffraction;
Characterization of ZnO structures by optical and X-ray methods by P. Petrik; B. Pollakowski; S. Zakel; T. Gumprecht; B. Beckhoff; M. Lemberger; Z. Labadi; Z. Baji; M. Jank; A. Nutsch (123-128).
► Comparison of optical and X-ray results on GaInZnO samples with Ga < 1 at%. ► Elemental composition determined by reference-free X-ray fluorescence. ► Correlation of the Raman-active dopant mode from Ga at 580 cm−1 with the Ga concentration. ► Surface nanoroughness taken into account for determination of accurate optical properties. ► Both the peak amplitude and the gap energy of ϵ 2 increase as a result of annealing and decrease with increasing Ga content.ZnO thin films doped by Ga and In as well as multilayer structures of ZnO/Al2O3 have been investigated by X-ray fluorescence, Raman spectrometry, spectroscopic ellipsometry and vacuum ultra violet reflectometry. Systematic changes in the optical properties have been revealed even for Ga concentrations below 1%. The Raman active phonon mode of Ga doping at 580 cm−1 shows a correlation with the Ga concentration. Optical models with surface nanoroughness correction and different parameterizations of the dielectric function have been investigated. There was a good agreement between the dielectric functions determined by the Herzinger–Johs polynomial parameterization and by direct inversion. It has been shown that the correction of the nanoroughness significantly influences the accuracy of the determination of the layer properties. The band gap and peak amplitude of the imaginary part of the dielectric function corresponding to the excitonic transition changes systematically with the Ga-content and with annealing even for low concentrations.
Keywords: Zinc oxide; Spectroscopic ellipsometry; X-ray fluorescence; Raman spectrometry; VUV reflectometry; Atomic layer deposition; Sputtering;